The RACAL RA17 receiver.

Recently I
had the good fortune to acquire a RACAL RA17 for myself. This particular set
seems to have had several owners and I've been told it originally started it's life at
Radio
Australia. Along the way it has suffered it's share of distress and
modifications that required a little
work to resolve.

What's so good
about them?

For me, the key to their
appeal is three-fold.

The first lies in their application of the
Wadley Loop. This effectively means they
have incredible frequency stability and tuning accuracy for a receiver of it's
time. The overall frequency stability of this set is governed by one single
crystal. Something unheard of at that time. The RA17 was the first
mass produced set to use the Wadley Loop.

The tuning mechanism is another
attraction. The design of the dial allows for
easy setting to within 1 KHz. This was amazing for a time where frequency counters were not
normal on receivers.

Finally, their construction. There's something about
a radio that's built like a tank that really appeals.

These sets saw
extensive use in the armed forces in many parts of the world. They were also used by
government agencies, embassies, coast watch stations, shortwave broadcasters and
frequency regulatory agencies around the world. Many, like mine, remained in
service until the 1980's and will continue to provide great service into the new
century for their lucky owners. Not bad for a set that ceased production in
1962.

The first thing to
remember about sets like this is that they are probably vastly different from
anything you have ever seen or used before. If you're any younger than forty it is
highly unlikely that your radio experience would include something like this.
Your experience with radios possibly amounts to tuning in the shortwave or ham
bands on a dual conversions radio (tube or semi) by tuning up and down a tiny
little dial
and selecting the appropriate mode (am, cw ssb). Or, it could be as simple as
punching in a frequency on a digital receiver or spinning the dial until the
digital display shows the frequency of interest. Not that there's anything wrong
with that. That's progress.

These sets need to
be operated with care and finesse to get the best out of them. If you want to
flick the set on and hear music and not fiddle about then this may not be the
best set for you. If on the other hand you love valve gear and love the
technology of it all and tweaking to get the best out of a radio then this is
the one for you.

Using the RACAL RA17.

To familiarize
myself with the set I followed the operations guide in the service manual.
There are a number of major
differences between this set and a many of today's more modern sets. Spending a
little time thinking about the set and it's functions will pay dividends later
on.

Kilocycle tuning.

The KHz tuning dial
is flywheel weighted and it takes almost one complete revolution of the dial to
travel 100 KHz. The KHz tuning
scale of the RA17 is made from something like 35mm film and is calibrated in
major increments of 10KHz along with minor increments of 5KHz and 1 KHz. The
50KHz and 100 KHz points and the 0 KHz and 1000 KHz are also clearly
indicated. A mechanical cursor adjustment is built into the dial escutcheon to
permit accurate calibration. At a glance it is a simple matter to identify your
receive frequency to the nearest KHz within any 1 MHz band.

Six foot tuning dial?

The manual quotes an effective dial
length of 145 feet. What does this mean? The distance between any two 100KHz
points on the dial scale is six inches. If you had a continuous dial scale with
the resolution of 6 inches per 100KHz, it would have to be 145 feet long if you were
to tune from 1MHz to 30MHz. Consider that
with some general purpose SW receivers you might go from 2MHz to 6MHz when you
tune the dial six inches and you can start to see the appeal of a set like this.

What does the RED scale indicate?

The red scale is
used in conjunction with the RA37 and RA137 LF Adapters. This allows the RA17 to
tune from 10KHz to 980KHz. Unfortunately, due to the frequency conversion scheme
used by these adapters the set tunes backwards when tuning below 1MHz.
For this reason, you will find the red scale is a mirror image of the normal
tuning scale.

But the scale goes to zero anyway?

True, but according
to the manual performance below 1MHz down to 500KHz is possible with "slight
degradation of performance". I've tested mine down to around 200KHz listening
for non directional beacons (NDB) and found that it works OK but there is a definite drop off
in performance at frequencies below 500KHz. I think the reason the manual quotes degraded performance
is because there is no facility on the pre-selector for frequencies below 500KHz.

Tuning linearity.

Whilst the
film scale is linear it's clear that no analog tuning system could ever hope
to match the linearity of a scale that is 5 feet long. RACAL included a
100KHz calibrator to allow for slight tuning variations. Basically you
tune the KHz dial to the 100 KHz point closest to your frequency of interest and zero beat
to the internally generated 100KHz calibration signal. Once you have zero beat,
manually adjust the KHz cursor on the escutcheon to coincide with the 100 KHz point on the film
scale. The kilocycle dial is now calibrated. In this way you minimize tuning
errors. I calibrated my receiver at the 500 KHz point on the dial and found that
the maximum error at 1000KHz was -1.5 KHz and at 0KHz it was +1 KHz. This means that
for most of the tuning range on my receiver the reading error will remain under
1000 cycles. Not bad considering the set was last calibrated in 1986.

Megacycle tuning.

The megacycle dial is simply marked in one MHz increments from 0 to 29 MHz.
Select the Mhz band of interest and that's it. Away you go. The tuning system on
the racal is amazing. This would have to be the easiest tuning system I have
ever used.
This is all due to the Wadley loop design. One dial for Mhz and one for KHz. You
can't get much simpler than that.

Dial Lock.

Because the tuning is so smooth and easy to turn, RACAL included a dial lock to
protect against accidental bumping. It's a simple friction lock that pushes a
rubber stopper against the dial mechanism for both the KHz and MHz dials.

Best tuning system ever?

In later
years a number of manufacturers incorporated the Wadley Loop into their design.
Amongst the more famous sets available to the public were the Barlow/Wadley
XCR-30 and the Yaesu FRG-7. In my opinion the "one dial for Mhz and one
dial for KHz" system is clearly the most elegant and simple arrangement ever
conceived.

Pre-selector and Attenuator.

The RA17 has a
five band pre-selector including a wide-band setting. The pre-selector is not
often seen in modern receivers and is used to manually tune the input of the
receiver to the desired receive frequency. Frequencies outside the range of the
pre-selector are severely attenuated. The wideband setting is used to by-pass
the pre-selector when searching over a large range of frequencies. Situated just
below the pre-selector is the attenuator. This is a five step attenuator
allowing 0 - 40db of attenuation in 10db steps. Careful use of the pre-selector
and attenuator will help avoid cross-modulation where strong unwanted signals
are present near the frequency of interest.

Signal Meter.

The signal meter
can be switched to shows
either AF output or RF level. When set to AF, the audio output level for an external 600Ω
output is monitored. This output was designed to be connected to a landline in
the case where the receiver may have been installed at a remote listening post.
The monitored AF level can be controlled via a screwdriver adjustment hidden
under the MHz dial. When switched to RF, the meter shows the current passing
through the detector diode. In this way the meter can be used as a rudimentary
albeit un-calibrated signal strength
indicator. RA17's destined for the American market also included and S-meter
setting that was calibrated in 4db per s-point increments.

The BFO.

The B.F.O. uses a reduction drive to
allow accurate setting of the B.F.O. frequency over a range of ± 8kc/s. The B.F.O. is
exactly tuned to a central point on the I.F. amplifier response when B.F.O. NOTE
KC/S control is set to zero-beat
with the check bfo function on the calibrator.

Having standardized the B.F.O. frequency, the frequency of
an incoming signal may be accurately measured by setting the KILOCYCLES control
to a zero-beat position. The B.F.O. should be detuned in order to produce an
acceptable note for c.w. and ssb
reception.

A.V.C. - Automatic Volume Control.

AVC is designed to keep the audio output level regardless of the signal strength
of the received signal. It does this by adjusting the receiver gain depending on
the strength of the incoming signal. In the RA17, the BFO is injected into the
detector, this has the effect of reducing the
receiver gain (sensitivity) because the AVC reacts to the BFO signal as it would
to any other received signal. Trying to resolve strong SSB signal
under these conditions can be very difficult if not impossible. CW reception is
not much better. To get around this problem the designers made it
possible to disable the AVC and
control the receiver gain manually. With
judicious use of the RF/IF gain control and AF level the results for both SSB
and CW can be very
satisfying. The AVC has a switchable long and short time constant. The
choice of time constants depends largely on conditions.

Using manual gain.

Using a receiver
with manual gain control is strange at first but once you've fiddled with it for
a while it becomes much easier. The first thing to do is back the RF/IF gain
right off and open the AF level right up. You may hear the audio change and
become harsh as you do this. Adjust the AF level to just below the point where
the harshness sets in. Your AF level is now set correctly. The audio output will
now be controlled solely by the RF/IF gain control. Now bring the RF/IF gain up
until you can hear signals at a reasonable level. With my set I found the best
results were achieved with a detector current of 80 - 100 uA as show on the
meter. Tuning around the bands is a
bit of an experience. It's quiet compared to tuning with AVC. Remember that AVC
controls receiver gain to try and
maintain a constant audio output. With manual gain you are in charge and must
ensure that the gain control is at it's optimum setting. Have the gain set too
low and you might miss a faint signal. Have the gain set too high and you may
overload the receiver. Using manual gain requires patience and a light touch but
once mastered becomes second nature.

Limiter.

The limiter on
this set is particularly effective with impulse noise. Electric fence or gas
starter noises are almost completely eliminated. The limiter works by
clipping any signal exceeding modulation peaks of 30%. Using the limiter when
listening to
good quality signals will result in deterioration of the recovered audio. As it says
in the manual "It does not introduce noticeable distortion below a 30%
modulation level". Maybe it should read "It will introduce noticeable distortion
for signals with greater than 30% modulation level". Still, if you are listening
to faint signals this might just make the difference between making the copy or
losing it.

Bandwidth Selection.

Six bandwidths are provided as follows:-

13 kc/s, 6.5 kc/s, 3 kc/s and 1.2 kc/s
(L-C filter)

300 c/s and 100 c/s (crystal filter)

The two crystal filters determining the
narrowest bandwidths are adjusted to ensure that their centre frequencies are within
50 c/s of each other, it follows that
any filter width can be selected without retuning the receiver. The 13 kc/s and 6.5 kc/s
settings are great for listening to A.M. signals.

The Speaker.

If there is one thing that disappoints
about this set - it has to be the speaker. There is a 2.5 inch speaker on the
front panel that could be used to monitor the receiver output. I doubt anyone
could bear to listen to that speaker for more than half an hour. The response,
understandably, is awful. Clearly in a monitoring situation the line out or
headphone output are much preferred. I imagine that the designers felt the
speaker would only be used during the initial installation of the set and as
such did not need to be anything special. Good idea back then, too bad for us.
An external speaker does wonders for this set.

On the air.

On air
tests show a great receiver that is quite capable of matching performance with
today's modern receiver.

Frequency stability and accuracy is
excellent.
On initial testing I came across a QSO on 40M and I was able to determine the
frequency of the stations as 7085.2 on the RACAL. A quick check on my Kenwood
R-2000 and Yaesu FRG-8800 showed the same result. There is no discernable drift
over an extended period of listening.

Sensitivity is great and the RACAL can
hear everything that my R-2000 and FRG-8800 can hear.

In the selectivity department I think the
RACAL is ahead. With careful use of the pre-selector and manual gain I feel the
RACAL just edges out the two more modern receivers.

Recovered audio is not as good as the
R-2000 but I feel the Kenwood audio is very hard to beat. The audio from the
RACAL is certainly of a high enough standard to allow listening over an extended
period - as long as you use a decent speaker!

Overall a wonderful receiver that is just
as good if not better than many modern receivers.

References

These few links I
think will help you gain a greater understanding into the world of the
Barlow-Wadley loop and RACAL and it's receivers. There are other sites to visit
but these are my best picks.